GSM modem means wireless serial connections

By now, most of us have seen have seen one of those GSM to wi-fi hotspot bridges. They’re interesting devices, and being able to carry a small wireless router with you at all times is very handy. Surprisingly, we haven’t seen many builds featuring these portable wireless hotspots, something probably due to the effort in breaking out a serial connection on these devices. The people at Open Electronics decided to build their own small serial-enabled cell phone modem, a boon to someone wanting a serial connection to any place with a cell tower.

The Open Electronics GSM/GPRS/GPS modem includes a header for an FTDI USB serial chip and a GSM module. Plug one into your computer and after a few short commands into a terminal, you’ve got a serial connection to nearly anywhere in the world.

The cost of the setup is a little high – around 80€ or $100 USD – and you probably should buy more than one so you can also receive data. While it is more expensive than the XBee wireless boards we see often, this GSM modem isn’t limited to the 300 foot range of the XBee. We’ll probably see this in a high altitude balloon before too long.

The prepaid cell phones are mass produced. Also the future phone card purchases make the original handset cheaper. The gsm serial device isn’t in a high demand and doesn’t have a large market Yet, also the gsm serial device doesn’t make any more money (phone cards)

The current v1.5 versions are advertised to have 1000 meter range, but I’d put money on them going further.

I’ve got a couple of the v1.5 units here ready to test against the old v1.3 units, just need to finish off the new test code which will enable swapping between the two units remotely so I can also gather dB connection data of the two.

In most of that video the rover is over the brow of a hill!
My main problem is the digital 2.4Ghz camera is swamping the XBee and the XBee trashes my analogue camera TX/RX.

In the turkey barns I’m transmitting temperature and humidity data from inside a big faraday cage back to the house.
It’s way more than 300′.
I guess they need to be a bit conservative with their range claims.

How do you go about wiring this up? And getting the modems to talk to each other? I’ve been looking for a way to do something like this just as something to play around with. Would be more interesting if you could use off-the-shelf 56K serial modems.

As someone that is using a commercial version of this you are either going to have to go with a data plan or try and get on a M2M provider. Both are going to be costly but an M2M (Machine 2 Machine), such as Kore Telematics, can be cheaper if you are doing very small data. Oh and this is about the same cost as the modem we are using.

High altitude balloon use will be pretty disappointing. Very little RF energy radiates upwards from GSM base stations. In fact the anteanae are optimised to radiate as much of the signal to where it needed – at ground level. Even tall buildings are without decent coverage until the an antenna is aimed at the building.

True even land mobile base/repeater antenna installations often are designed to have a down tilt in the pattern. However at higher altitudes because of the Earth’s curvature may be looking into some distant cell phone towers, the the question becomes if the distance is too great so signal levels are inadequate. An interesting paper exercise to do sometime I guess.

No doubt there are those who can’t be bothered becoming licensed are surely all ready using packet radio for high altitude balloon telemetry and are equally less likely to spend this kind of money be on the lawful side of things. Those who know what they are doing, and can build a clean transmitter run little risk of getting caught, even though the foot print can be pretty big. Not that I’m recommending anyone do so.

Fair enough @n0lkk
I already came up with a workaround for licensing, use light.
No restrictions on that, apart from you have to ensure it is safe for eyes ie defocussed.
IIRC the standard says it has to be under 0.8mW in an 8mm diameter beam to be classed as “eye safe”.
Which means most commercial LED torches are actually dangerous if you stare into the beam!

A little tip, optical laser mice use a 1mA 0.7mW VCSEL which puts out a nice beam that is ideal for tracking etc. See notes above..

An inserting idea, but wouldn’t that be a small footprint on the Earth surface, that would be doing didos as the payload swings on the tether? Could be hell for the recovery teams to keep track of the balloons position. Many of these flights carry student payloads, who would want to receive their telemetry without having to chase down the footprint. Then there’s attenuation by water vapor. RF provides a back up means of tracking if something happens to the GPS telemetry.

Cellular data plans are capped at notoriously low levels and cost way too much for anything but a trickling flow of data. Exceed the cap – and they hook a vacuum cleaner to your wallet and turn it on!

Finally, you either have to pay a monthly recurring subscription fee, or constantly recharge a pre-paid SIM card. With the pre-paid cards, typically you lose your number if you don’t recharge the card regularly, whether you need to or not. With the pre-paid cards, your credits often expire if not used withing a certain time window (money lost forever).

The whole greedy data-plan marketing and business model used by the cellular operators has made me swear-off using them – ever!

Anyways…as nifty and fun it may feel to enable devices to communicate together wirelessly….or any ingenious intuitive invention or collaboration for that matter… I think we as humans needa re evaluate what we do with our time. I dunno tho I’m tired as fuck.

Simple way around the prepay problem is to have it automatically send one SMS per week (or whatever the requirement is) via a timer.
Also the ones available here usually tell you when you dial the topup number when the credit is due to expire.

Also, another way around the data cap. Encode the data using high compression, as the cap is per MB *sent* not per MB uncompressed.
This is used on some PCs to get around SATA latency and SSD limitations.
You take a performance hit but for most applications such as sending video frames its a small price to pay for less $ spent.

OpenWrt, a cheap router (TP-Link TL-WR3220) and a cheap USB UMTS stick seems a good alternative: you gain all capabilities from having a full-blown computer, you can connect more or less anything that has a USB port, plus it doubles as a WiFi base station or client. Purchase price is the same or less, but you need to shop around for a good data deal. At least in Europe, you can find pre-paid and post paid contracts with short terms that cost only a few Euros a month and include a small amount of data (up to 100 MB) for free; plenty if all you want to do is access a serial device every once in a while. Only drawback is the power requirements.

Currently in Poland we have FREE 256kbit UMTS internet (till 21.12.2014) due to surprisingly beneficial (to the people, not corporations :o) radio license LTE opeator had to agree upon when buying the band.

Here is a GSM/GPRS / Arduino development board I’ve been playing with recently. It’s an Arduino board with a GSM radio built in. It’s useful for projects that you want to control via SMS message, or you want it to send you messages when a sensor reads a value.